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Data Event Response to the 21 July 2015 Mw 4.0 Earthquake 3km NNE of Fremont, California

Written by David Phillips & Beth Bartel
10 September 2015

Tectonic Summary

From the USGS Event Page:
37.577°N 121.974°W depth=8.4 km (5.2 mi)

The Hayward Fault is a mostly right-lateral, strike-slip fault with approximately 5 mm/yr (1/5 inch/year) of creep. The 2003 Working Group for California Earthquake Probability, in agreement with previous working groups going back to 1990, assigned a slip rate on the Hayward Fault to be about 9 mm/yr (1/3 inch/year). This implies that approximately 4 mm/yr of motion is taken up in a stick-slip fashion, leading to the generation of earthquakes.

The Hayward Fault runs from San Pablo Bay in the north to Fremont in the south, passing through the cities of Berkeley, Oakland, Hayward, and Fremont. South of Fremont the fault branches into a complex set of surface faults that connect the Hayward Fault to the central part of the Calaveras Fault. The Hayward and Calaveras Faults may have a simpler connection at depths more than 5 km (3 miles), joining in the subsurface just south of the Calaveras Reservoir (site of the October 30, 2007 M5.4 Alum Rock earthquake). The Hayward Fault may be segmented into a northern and southern segment in the vicinity of Berkeley or Oakland.

For more information, see the USGS Earthquake Hazards Program event page.

UNAVCO Response

GPS data
In response to the Mw 4.4 Earthquake 3km NNE of Fremont, California on July 21, 2015, five-sample-per-second (5-sps or 5-Hz) GPS data were collected for a 3-day period around the event (day of event ± 1 day). The data are available from ftp://data-out.unavco.org/pub/highrate/.

Stations downloaded:

GPS velocities
The GAGE GPS Analysis Center Coordinator estimates coseismic offsets for any stations that experience horizontal displacements of > 1mm. If such offsets are observed, station offset files are made available from ftp://data-out.unavco.org/pub/products/event/. No such offsets were observed for this event.

Borehole strainmeter data
UNAVCO produced a fully processed 1-sps borehole strainmeter (BSM) dataset spanning the time period of this event, made available at http://borehole.unavco.org/bsm/earthquakes/20150721_FremontCalifornia/.

Borehole seismic data
PBO seismic data (1-sps and 100-sps) are available from the IRIS DMC under the network code “PB.” PBO seismic data can be accessed from http://www.unavco.org/data/strain-seismic/seismic-data/seismic-data.html and http://ds.iris.edu/ds/nodes/dmc/data/types/waveform-data/.

UNAVCO Data and Support

  • Please contact archive-gpsunavco.org for information on data availability

Related Links

Map Center:
Fremont, California


Last modified: 2020-02-06  01:05:05  America/Denver